Global Warming on Mars

Artificial greenhouse gases that are bad news on
Earth could provide the means to make Mars a more comfortable
place for humans to live.

February
9, 2001 -- To say that Mars is a chilly place would be an
understatement. The Red Planet's mean annual temperature is 55
degrees C below zero -- that's about the same as the temperature
of Earth's south pole during winter.

If humans ever build communities on Mars, they might want
to find a way to turn up the global thermostat. At a recent NASA-sponsored
conference, "The
Physics and Biology of Making Mars Habitable", scientists
discussed ways that future colonists might make the frigid planet
a little more comfortable.

One solution might be to pump enough greenhouse gases into
the Martian atmosphere to create a runaway greenhouse effect.
Here on Earth, the idea of a runaway greenhouse sets off alarm
bells. But on Mars it could be a plus. Scientists at the conference
speculated how it might be possible to warm Mars just enough
to evaporate the planet's available carbon dioxide (CO2
trapped in ices and frost) into the atmosphere, where such gases
could contribute to keeping the planet warm.

But there are two problems. First, even if all of Mars's
available CO2 were coaxed into the atmosphere, it
wouldn't necessarily warm the planet enough to make it a comfortable
place for humans, because no one knows just how much CO2
is there. Second, the best way to get Mars to release its CO2
spontaneously is, well... to warm it up. It's a "Catch-22"
situation!

Margarita
Marinova, an undergraduate student at MIT, believes she has
an answer to both problems: use artificially created perfluorocarbons
(PFCs) to initiate the planetary warming process. Marinova has
been studying the warming effects of PFCs, in collaboration with
Chris McKay, a member of the NASA Astrobiology
Institute at the Ames Research Center. McKay was one
of the organizers of the terraforming conference where Marinova
presented her research.

PFCs have several advantages. First, they are super-greenhouse
gases. A little bit does a lot of warming. Second, PFCs have
a very long lifetime. This causes serious
problems on Earth, but their longevity would be a positive
factor on Mars. Third, they do not have any negative effects
on living organisms.

Finally, unlike their chemical cousins, chlorofluorocarbons
(CFCs), PFCs don't deplete ozone. Ozone in Earth's atmosphere
provides protection against ultraviolet (UV) radiation, which
is harmful to life. On Mars, building up an ozone layer in the
atmosphere would be an important goal of terraformers. "You
don't want to destroy ozone," says Marinova, "because
it's a UV protector."

Above: Sunlight is absorbed by a planet's
surface, which then radiates warming infrared energy into the
atmosphere. Greenhouse gases prevent that energy from escaping
into space.

The sunlight that hits a planet's surface arrives primarily
as visible and ultraviolet light. The planet absorbs this solar
energy, and then re-radiates warming infrared energy back out
into the atmosphere. Greenhouse gases in the atmosphere work
as a global layer of insulation, trapping that infrared radiation
and preventing it from escaping into space.

CO2 and water are good at trapping some of this
infrared energy, but not all of it. On Earth, there's so much
CO2 and water in the atmosphere that it doesn't matter
if some infrared radiation escapes back into space.

But on Mars, terraformers will want to trap every bit of heat
they can. A carefully chosen combination of PFCs could do the
job quite handily.

"When we first start warming Mars," explains Marinova,
"we'll want to cover the whole spectrum" of thermal
infrared radiation. "Once CO2 is released, it
will take over" part of the job, and PFCs will only need
to be used to plug the gaps.

And how fast can Mars be heated up?

"That depends," says Marinova, "on how fast
we make the gases." According to rough calculations, "if
you had 100 factories, each having the energy of a nuclear reactor,
working for 100 years, you could warm Mars six to eight degrees."
At that rate, to increase the average Martian temperature to
the melting point of water -- it's about minus 55 degrees Celsius
now -- would take about eight centuries. Actually, it wouldn't
take quite that long, Marinova points out, because her calculation
doesn't include the feedback effect of the CO2 that
would be released as Mars got steadily warmer. "Devising
more efficient artificial super-greenhouse gases will also make
it faster," Marinova adds.

Above: Though still an undergraduate
student, Margarita Marinova is advancing our understanding of
how to make Mars habitable for humans. Pictured with her is Phobos,
a teammate from the Haughton-Mars expedition to the Arctic. Image
courtesy The Mars Society.

Human habitation of Mars is a long way off. NASA's current
plan for exploring the Red Planet, which spans the next two
decades, does not include even a pioneering human mission to
Mars. By the time a permanent settlement is established there
-- one that might begin the task of terraforming the planet --
technological advances may make it possible to warm its atmosphere
far more efficiently than is possible using the techniques being
studied today by scientists like Marinova.

Editor's note: We recently published an
article explaining how the solar wind is able to erode Mars's
atmosphere because the Red Planet does not have a protective
magnetosphere. Will future terraformers need to establish a global
magnetic field on Mars to protect any atmosphere they create?
Not necessarily. The planet Venus, for instance, has a chokingly
thick atmosphere, but no magnetic field to protect it against
the wind from the nearby Sun. Every planetary atmosphere is a
balance between "sources and sinks." If some process
(like volcanism) pumps gas into the atmosphere at a rate that
substantially exceeds solar wind loses, the atmosphere will persist.
The equilibrium on Venus happens to favor a thick atmosphere.

Outpacing solar wind erosion will be one of many challenges that
future colonists might face. Fortunately, though, the solar wind
is less powerful now because of stellar evolution than it was
billions of years ago when the Red Planet presumably lost most
of its air. That might give the needed edge to the terraformers!
--Tony Phillips

The Science and Technology Directorate at NASA's
Marshall Space Flight Center
sponsors the Science@NASA web sites. The mission of Science@NASA is to
help the public understand how exciting NASA research is and to help
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